1. Field of the Disclosure
The disclosure relates to a power converter, more particularly, to a power converter having a low electromagnetic interference (EMI).
2. Description of Related Art
A power converter is used for converting unregulated power into a regulated voltage or current. Generally, a control circuit in the power converter can generate a switch signal to regulate an output voltage or current of the power converter, so as to adjust and stabilize the power of the power converter. Wherein, a duty cycle of the switch signal is modulated according to the output of the power converter, and a switching frequency of the switch signal is generally self-determined in internal of the control circuit of the power converter. In recent developments, a lot of pulse width modulation (PWM) control circuits are developed for the power converter in order to save the power consumption.
The power converters can be divided into linear power converters and switching power converters according to different circuit structures thereof. Wherein, the circuit structure of the switching power converter is complicated compared to that of the linear power converter, and electromagnetic interference (EMI) thereof is relatively great, though the switching power converter has advantages of high conversion rate, low power consumption during an idle state, and light-weight. In overall, the switching power converter is better than the linear power converter, so that the switching power converter is popular in a current power converter market. However, the EMI generated by the switching power converter can cause a noise of the power supply to influence other electronic devices, and can also influence signal transmissions of the neighboring communication devices or radios and televisions due to an outgoing radiation.
A conventional method for reducing the EMI is to add an EMI filter at an input terminal of the power supply. The EMI filter is generally consisted of passive devices such as inductors, capacitors and resistors, etc., so as to implement a purpose of filtering the EMI. However, the greater the EMI is, the greater the required EMI filter is, so that not only a circuit cost is increased, but also the EMI filter cannot deal with the radiation of the EMI.